The problem with Diablo 3's skills

Over the past few days I've been thinking about which classes I will play when Diablo 3 ships, what builds they will have and what equipment they'll wear. I realized that there are some major issues with the way skills and equipment interact. I am stumped at this point and if anyone can clear a few points for me, I'd be grateful.

Compared to other RPGs and even Diablo 2, Diablo 3's skills are independent of equipment. There are no weapon/armor specializations. Whether you are a Barb with a bow, 1H sword, 2H axe or spear, your character will have access to the same skills and spells. This, to me, feels weird.

In a way, it greatly simplifies the skill system because you won't have to spend countless hours agonizing about whether to pick an axe build or a sword build. On the other hand, certain aspects of this system are very confusing to me.

Take the Barbarian, Monk or Witch Doctor. They can equip either one of the following:
- 1H weapon + shield
- 2H weapon
- dual-wield 1H weapons

Most offensive spells and skills are based on weapon damage. Here are my questions:

How the hell is damage calculated for 2H weapon vs dual-wield 1H weapons? I'm sure this has been explained at some point by the devs but I missed it. It should be fairly obvious, yet I don't know what the answer is.

In which situations is it preferable to wear a 1H weapon + shield instead of 2H weapon or dual-wielding? Since skill damage is derived from weapon DPS, it is obvious that equipping a shield would greatly gimp your overall damage. In addition, there doesn't seem to be any advantage to wearing a shield, except for a little bit of extra mitigation, which is probably insignificant, thanks to the fact that there are no skills which enhance your shield abilities or give you any incentive to equip a shield.

Considering the above point, why are shields even in the game?

If spells and skills are based on weapon damage, won't a spellcaster pick the hugest 2H weapon she can find? Are we going to see Wizards running around with massive 2H axes? Blizzard mentioned at some point that there will be advantages to equipping two items instead of one but this whole thing feels like lazy design to me, not to mention that for some classes it simply doesn't make any sense to base their spell damage on weapon damage. I'm looking at you, spellcasters.

Playing Path of Exile made me realize what huge difference there is between that game and Diablo 3. In Path of Exile you can create a build specifically for 1H sword + shield, or 1H mace + shield, or 2H axe or dual-wield maces, just to give a few examples. I'm not a big fan of pigeonholing a character into using only certain types of weapons, but I do wish there was an advantage to using a certain type of gear combo compared to another, based on the skills you are using.

My final word is that shields seem useless to me and I will probably go with the highest DPS weapon combo I can find, but I'm still not satisfied with the way things are. I wish they'd done it a different way.